Introduction FF10502-01 is a synthetic pyrimidine nucleoside analogue that is structurally similar to gemcitabine (GEM) with a substitution of sulfur for oxygen in the pentose ring. FF-10502-01 demonstrated potent anti-tumor activity in a number of preclinical studies. In both Capan-1 and SUIT-2 pancreatic cancer xenograft models, FF-10502-01 achieved superior tumor growth suppression and survival prolongation, respectively, compared to GEM, with less toxicity at clinically relevant doses. In GEM-resistant pancreatic PDX models, FF-10502-01 showed greater efficacy and tolerability than GEM. A Phase 1 trial of FF-10502-01 in patients with advanced cancer has been conducted in United States with positive results, and a Phase 2a trial is scheduled for 2018.

Methods To determine the putative differences between FF-10502-01 and GEM activity the following studies were undertaken. The inhibitory activity for polymerase alpha and beta was measured using a DNA synthesis assay in vitro. Purified human polymerases and tri-phosphates of test drugs were incubated for 30 minutes at 37 °C in the presence of [methyl-3H]dTTP, and radioactivity was measured by liquid scintillation counting. SUIT-2 cells were cultured in serum-free medium for 72 hours to establish a dormant cell model. The test drugs, with DNA damage inducers, were then added as combination treatment. After 72 hours, the cell growth inhibition was evaluated using an ATP cell viability assay. DNA damage in the dormant cell model was evaluated by alkaline comet assay.

Results To explain why FF-10502-01 was more potent than GEM in vivo, we investigated possible differences in their mechanisms of action (MOA). Both FF-10502-01 and GEM inhibited DNA replication in vitro and in vivo. On the other hand, only FF-10502-01 showed potent cytotoxic activity against serum starvation-induced dormant SUIT-2 cells in combination with DNA damage inducers (DDIs: H2O2, cisplatin, or temozolomide). Similar results were obtained in cholangiocarcinoma and ovarian cancer cell lines. In vitro enzymatic assays showed that FF-10502-01 was far more potent than GEM in inhibiting DNA polymerase-beta, which plays an essential role in repairing oxidative DNA damage via the base-excision repair pathway. The inhibitory activity of DNA repair may explain the differential effect of FF-10502-01 in solid tumors in which reactive oxygen species are generated by tumor specific microenvironment.

Conclusions Unlike GEM, FF-10502 is unique in preventing DNA repair via polymerase-beta inhibition when combined with DDIs, suggesting a dual MOA for FF-10502 in solid tumors compared to GEM.

Citation Format: Kazunori Saeki, Rena Uematsu, Kaoru Morimura, Takayuki Yamada, Hiroyuki Iwamura, Shinichi Watanabe, Timothy Madden, Shinji Hagiwara. A novel antimetabolite, FF-10502-01 exhibits potent antitumor activity via inhibition of both DNA replication and DNA damage repair in solid tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 326.